Method and system for frequency hopping radio communication

ABSTRACT

A transmitter shown in FIG.  3  inputs to a mixer  36  an IF band modulation signal generated from transmission data and a frequency hopping signal obtained by a hopping synthesizer  38  controlled by a hopping pattern generator  37 , thereby obtaining a frequency hopping radio signal to be transmitted. In a receiver shown in FIG.  4,  a received signal is amplified and an unnecessary wave is removed from the signal, and the resultant signal is input to a mixer  44 . The mixer  44  receives an output signal of a hopping synthesizer  47  controlled by a signal obtained by adding a fixed frequency offset signal to the hopping pattern generator  45 . A signal downconverted to a first IF band without frequency hopping corresponding to the offset signal with a radio frequency band signal maintaining the relative spectrum relationship appears in the output of the mixer  44 . An unnecessary wave of the signal is removed, a square unit  49  performs square detection, and a modulation signal in the intermediate frequency band used by the source is regenerated. The obtained IF band signal is modulated, thereby receiving desired data.

TECHNICAL FIELD

The present invention relates to a frequency hopping wirelesscommunication method and system for performing wireless communication towhich a frequency hopping system is applied in an area of a highfrequency such as a milliwave band, etc.

BACKGROUND ART

When a wireless communication system for use in a frequency bandrequiring no license, it is effective to implement a frequency hoppingsystem as means for avoiding or sufficiently suppressing the effect of anarrow-band interference.

FIGS. 6 and 7 show the configurations of the transmitter and thereceiver of a wireless communication system when a common frequencyhopping system is used. The transmitter obtains a frequency hoppingradio modulation signal by inputting to a mixer 4 a signal obtained froman intermediate frequency (IF) band modulator 1 for receivingtransmission data and an output of a hopping synthesizer 3 controlled bya signal from a hopping pattern generator 2. An unnecessary wavecomponent is removed from the signal by a band pass filter 5, and aresultant signal is transmitted from a transmitting antenna 6. In thereceiver, after a received signal is received by a receiving antenna 7and amplified by an amplifier 8, an unnecessary wave component isremoved by a wide band pass filter 9, the resultant signal and an outputsignal of a hopping synthesizer 12 controlled by a hopping patterngenerator 11 for generating a frequency hopping pattern corresponding toa desired received signal are input to a mixer 10, the signals passthrough a band pass filter 13, and a non-hopping fixed IF frequencymodulation signal is obtained. The signal is input to an IF banddemodulator 14, and the data is demodulated. FIG. 7 shows theconfiguration for capturing the synchronization of a hopping frequencyin the receiver. That is, the output of the band pass filter 13 furtherpasses through a signal detector (envelope detector) 15 and anintegrator 16, and is compared with a threshold level and input to aphase controller 18, and the output controls the generated phase of thehopping synthesizer 12.

In this case, to maintain the quality of the transmitted signal, and toobtain a substantial interference suppression effect by a frequencyhopping, it is necessary to maintain a predetermined frequencydifference between the output of the hopping synthesizer used in atransmitter and the output of the hopping synthesizer used in areceiver, and to maintain small time fluctuation for a phase difference.Therefore, it is necessary that the hopping synthesizer to be used in atransmitter and a receiver is stable in frequency, has low phase noise,and is highly responsive. Especially, in a high-frequency microwavearea, various methods for stabilization, lower noise, etc. using adielectric oscillator or a PLL (phase lock loop) are devised.

However, as the frequency becomes higher (for example, a milliwave bandof 30 GHz or more), it is more difficult to realize a frequency-stableand low phase noise hopping synthesizer, and the production cost rises.Furthermore, when a modulation signal to be transmitted is amulticarrier signal which is a narrow-band modulation signal or an OFDM(orthogonal frequency division multiplexing) signal, it is necessarythat the hopping synthesizer between a transmitter and a receiver has asynchronous frequency with high precision. Additionally, since thefrequency changes at a burst, a responsive countermeasure is required.However, it is very hard to operate in, for example, a high frequencysuch as a milliwave band a hopping synthesizer capable of synchronize afrequency with high precision, and it is also very difficult toimmediately take action against an occurrence of a large frequencyoffset or synchronously supplement it, thereby requiring an expensivesystem stabilizing mechanism.

DISCLOSURE OF THE INVENTION

The present invention has been developed to solve the above-mentionedproblems, and aims at configuring a wireless system in a frequencyhopping system free of the effect of a local oscillator for a frequencyconversion or the unstable frequency of a hopping synthesizer.

The present invention also aims at realizing a small and low-cost andsystem capable of applying without a highly stable local oscillator orhopping synthesizer a frequency hopping system in a very high frequencyarea such as a milliwave band in which the frequency hopping system hasconventionally been very difficult.

The frequency hopping wireless communication method and system accordingto the present invention performs communications between a plurality ofwireless communication terminals each including: a transmitting unit forgenerating a radio modulation signal by multiplying an intermediatefrequency band modulation signal from an intermediate frequency bandmodem by a local oscillation signal; and a receiving unit for generatingan intermediate frequency band demodulation signal downconverted bymultiplying a radio modulation signal by a local oscillation signal, anddemodulating the signal in the intermediate frequency band modem. Atransmitting station for transmitting only a reference local oscillationsignal is provided, or one of the plurality of wireless communicationterminals acts as a base station or a parent station and transmits alocal oscillation signal for use in the station together with a radiomodulation signal. Each of the plurality of wireless communicationterminals modulates a transmission signal in the frequency hoppingsystem using the intermediate frequency band modem, and demodulates areceived signal. Furthermore, each of the plurality of wirelesscommunication terminals receives a reference local oscillation signalfrom the transmitting station, amplifies and band filters the signal,regenerates a reference local oscillation signal by an injectionsynchronous oscillator or an amplifier, and mutually performscommunications using the signal as a local oscillation signal for use bya transmitting function and a receiving function.

According to the present invention, in each of the plurality of wirelesscommunication terminals, the transmitting unit upconverts a modulationsignal generated in an intermediate frequency band to a radio frequencyband using a local oscillation signal functioning as a hoppingsynthesizer, and simultaneously transmits a frequency hopping radiomodulation signal of a single-side band wave or a both-side band waveobtained by the upconversion and the local oscillation signal used inthe upconversion. The receiving unit downconverts a received signal to afirst intermediate frequency band signal using a local oscillationsignal frequency hopping in a pattern obtained by adding a fixedfrequency offset to a frequency hopping pattern corresponding to adesired reception wave, and then extracts two signal components, thatis, a local oscillation signal component and a modulation signalcomponent, by passing the downconverted signal through a band passfilter, and generates a product component of the two signal components,thereby regenerating a second intermediate frequency band modulationsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the first embodiment of the present invention;

FIG. 2 shows a spectrum transmitted/regenerated according to the firstembodiment;

FIG. 3 shows the configuration of the transmitter according to thesecond embodiment;

FIG. 4 shows the configuration of the receiver according to the secondembodiment;

FIG. 5 shows the spectrum transmitted/received according to the secondembodiment;

FIG. 6 shows the configuration of the transmitter in the conventionalfrequency hopping system; and

FIG. 7 shows the configuration of the receiver in the conventionalfrequency hopping system.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 shows the configuration of the wireless communication systemaccording to the first embodiment of the present invention. FIG. 2 showsthe transition os a signal spectrum transmitted and received by eachstation. As shown in FIG. 1C, the system comprises one reference signalstation 19 and a plurality of terminal stations 23. As shown in FIG. 1B,the reference signal station 19 amplifies the reference localoscillation signal generated by a reference station local oscillator 20using an amplifier 21, and then transmits the signal from an antenna 22.As shown in FIG. 1A, each terminal station 23 receives it using areceiving antenna 24. The received signal is amplified by an amplifier25, a part of the resultant signal is branched, a band pass filter 26removes an unnecessary wave, and the resultant signal is input to thesynchronous oscillator or an amplifier 27. As a result, a localoscillation signal synchronous with the reference local oscillationsignal output by the reference signal station 19 is obtained. Theterminal station 23 branches the obtained local oscillation signal intotwo, inputs one to a receiving frequency converter (mixer) 28, and theother to a transmitting frequency converter (mixer) 29. The mixers 28and 29 of the terminal station 23 are connected an intermediatefrequency (IF) band modem circuit 31 in the FH system for demodulatingand generating a signal in the frequency hopping system (FH). Anunnecessary wave component of an IF band FH modulation signal output bythe mixer 28 is removed by a band pass filter 30, and then the signal isinput to the intermediate frequency (IF) band modem circuit 31 in the FHsystem, thereby obtaining desired data. Meanwhile, the IF band FHmodulation signal obtained by the intermediate frequency (IF) band modemcircuit 31 is input to the mixer 29, and frequency-converted to a radiofrequency band. After an unnecessary wave is removed by a band passfilter 32, an amplifier 33 amplifies the signal, and transmits itthrough a transmitting antenna 34.

The configuration of the transmitter/receiver included in the IF bandmodem circuit 31 in the FH system is the same as that of theconventional frequency hopping system shown in FIGS. 6 and 7. Accordingto the first embodiment, the frequency offset and phase noise occurringin a radio signal are sufficiently removed by the circuit before it isinput to the intermediate frequency (IF) band modem circuit 31 in the FHsystem. Therefore, since the intermediate frequency (IF) band modemcircuit 31 in the FH system does not have to be highly responsive or toexcel in synchronous supplement, the conventional frequency hoppingsystem can be used.

FIG. 2 shows the transition a signal spectrum in time transmitted andreceived according to the first embodiment of the present invention.While the frequency of a spectrum (deep black portion) issued from thereference signal station 19 does not change with time, a radiomodulation signal (pale black portion) upconverted and transmitted usingthe reference local oscillation signal indicates frequency hopping withtime.

According to the first embodiment, a station for transmitting only areference local oscillation signal is provided in addition to aterminal. With the configuration, in a system in which the transmittingpower in aerial wire is limited for each transmitting station, moretransmitting power can be assigned to a reference local oscillationsignal, thereby successfully extending the communication area.

However, a reference local oscillation signal transmitting station canhave the function of a terminal or the function of transmitting andreceiving a signal. That is, one of the terminal group acts as a parentstation, transmits to space a local oscillation signal used by thestation as a reference local oscillation signal, and each of the otherwireless terminals receives the reference oscillation signal, amplifiesand band filters the signal, regenerates a local oscillation signalsynchronous with the reference local oscillation signal at anappropriate level by the injection synchronous oscillator, and definesit as a local oscillation signal for frequency conversion used in thetransmitting and receiving function.

In any case, according to the first embodiment, the configuration fortransmitting a reference local oscillation signal has the merit of beingfree of the effect of an unstable frequency of a local oscillator forfrequency conversion, thereby successfully configuring a wireless systemof the frequency hopping system without an effect of unstable frequencyof a local oscillator for frequency conversion.

Second Embodiment

FIGS. 3 and 4 show the configuration of a transmitter and theconfiguration of a receiver of the wireless communication systemaccording to the second embodiment of the present invention. FIG. 5shows the transition of the spectrum of a signal transmitted andreceived between terminals. The present invention can be applied to thecommunications between a plurality of wireless terminals, and eachwireless terminal comprises a transmitting unit as shown in FIG. 3 and areceiving unit as shown in FIG. 4, thereby performing bi-directionalcommunications.

The transmitter shown in FIG. 3 generates an IF band modulation signalusing an IF band modulator 35 and inputs an FH signal obtained by ahopping synthesizer 38 controlled by a hopping pattern generator 37 andthe IF band modulation signal to a mixer 36, thus obtains a frequencyhopping radio signal. The output includes an output signal of a hoppingsynthesizer used as a local oscillation signal in addition to the radiosignal of a both-side band wave whose frequency is converted as shown inFIG. 5. These signals are amplified by an amplifier 39, and transmittedthrough an antenna 40.

According to the present embodiment, when a both-side band wave signaland a local oscillation signal are transmitted as outputs of a mixer inthe present embodiment, etc., nothing to be removed by a band passfilter basically occurs. Therefore, as shown in FIG. 3, the band passfilter is not necessary after the frequency conversion mixer as shown inFIG. 3, thereby realizing a low-cost transmitter configuration.

Using an image rejecting mixer, a frequency-converted radio signal of asingle-side band wave and an output signal of a hopping synthesizer usedas a local oscillation signal can also be obtained.

In a receiver, a signal received by a receiving antenna 41 is amplifiedby an amplifier 42, an unnecessary wave of the signal is removed by aband pass filter 43, and the resultant signal is input to a mixer 44.Furthermore, the mixer 44 receives an output signal of a hoppingsynthesizer 47 controlled by a signal obtained by adding to a hoppingpattern generator 45 a fixed frequency offset signal by an offset signalgenerator 46. As a result, a signal downconverted to a first IF bandwithout frequency hopping corresponding to the offset signal with aradio frequency band signal maintaining the relative spectrumrelationship appears in the output of the mixer 44. An unnecessary waveof the signal is removed by a band pass filter 48, a square unit 49performs square detection, and a modulation signal in the intermediatefrequency band used by the source is regenerated. In this signal, nofrequency offset or degradation of phase noise occur in principle whenupconversion and downconversion to a milliwave band in the FH system areperformed because the original local oscillation signal component beforethe downconversion to the IF band and the radio modulation signalcomponent, which are input to the square unit 49, have the samefrequency offsets and phase noise components. Therefore, the obtained IFband signal is input to an IF band demodulator 50, and desired data canbe received. FIG. 4 also shows the configuration for capturingsynchronization of a hopping frequency in a receiver. That is, theoutput of the square unit 49 further passes through a signal detector(envelope detector) 51 and an integrator 52. The resultant signal iscompared with a threshold level by a threshold comparator 53 and inputto a phase controller 54. The output further controls the generatedphase of the hopping synthesizer 47.

As described above, according to the second embodiment, a wirelesssystem of the frequency hopping system without an effect of an unstablefrequency of a hopping synthesizer can be configured.

INDUSTRIAL APPLICABILITY

According to the present invention, a wireless system of the frequencyhopping system without an effect of a local oscillator for frequencyconversion or an unstable frequency of a hopping synthesizer can beconfigured, thereby applying a frequency hopping system in a very highfrequency area such as a milliwave band, etc. in which it has beenconventionally hard to apply the system. Since it is not necessary touse a highly stable local oscillator or hopping synthesizer, a small andlow-cost terminal and system can be realized.

1. A frequency hopping wireless communication method for performingcommunications in a frequency hopping system among a plurality ofwireless communication terminals, characterized in that: onetransmitting station transmitting a reference local oscillation signal;each of the plurality of wireless communication terminals modulates atransmission signal in the frequency hopping system using theintermediate frequency band modem, and demodulates a received signal;each of the plurality of wireless communication terminals receives thereference local oscillation signal from the transmitting station,amplifies and band filtering the signal, regenerates the reference localoscillation signal by an injection synchronous oscillator or anamplifier, and using the signal as a local oscillation signal for use bya transmitting function and a receiving function; generates a radiomodulation signal by multiplying an intermediate frequency bandmodulation signal from an intermediate frequency band modem by a localoscillation signal, and transmits the radio modulation signal; andgenerates an intermediate frequency band demodulation signaldownconverted by multiplying a radio modulation signal by a localoscillation signal, and demodulates the signal in the intermediatefrequency band modem.
 2. The frequency hopping wireless communicationmethod according to claim 1, further comprising one transmitting stationfor transmitting only the reference local oscillation signal.
 3. Thefrequency hopping wireless communication method according to claim 1,wherein one of the plurality of wireless communication terminals acts asa base station or a parent station and transmits a local oscillationsignal for use in the station together with a radio modulation signal,and each child station which is one of the other wireless communicationterminals receives a reference local oscillation signal transmitted bythe base station or the parent station.
 4. A frequency hopping wirelesscommunication method for performing communications in a frequencyhopping system among a plurality of wireless communication terminals,characterized in that: in the plurality of wireless communicationterminals, a transmitting unit inputs to a mixer a modulation signalgenerated in an intermediate frequency band and a frequency hoppingsignal obtained by a hopping synthesizer controlled by a hopping patterngenerator, and obtains a frequency hopping radio signal; and amplifiesan output signal of a hopping synthesizer used as a local oscillationsignal in addition to a frequency hopping radio modulation signal of asingle-side band wave or a both-side band wave by an amplifier without aband pass filter, and transmits the signal through an antenna, and thereceiving unit of the wireless communication terminal downconverts areceived signal to a first intermediate frequency band signal using alocal oscillation signal frequency hopping in a pattern obtained byadding a fixed frequency offset to a frequency hopping patterncorresponding to a desired received wave, and then, extracts two signalcomponents, that is, a local oscillation signal component and amodulation signal component, by passing the downconverted signal througha band pass filter and generates a product component of the two signalcomponents, thereby regenerating a second intermediate frequency bandmodulation signal.
 5. A frequency hopping wireless communication systemfor performing communications in a frequency hopping system among aplurality of wireless communication terminals, comprising: atransmitting station for transmitting a reference local oscillationsignal; and a plurality of wireless communication terminals each havingan intermediate frequency band modem for modulating a transmissionsignal using the frequency hopping system and demodulating a receivedsignal, wherein each of the plurality of wireless communicationterminals includes: a transmitting unit for receiving the referencelocal oscillation signal from the transmitting station, amplifying andband filtering the signal, regenerating the reference local oscillationsignal by an injection synchronous oscillator or an amplifier, using thesignal as a local oscillation signal for use by a transmitting functionand a receiving function, generating a radio modulation signal bymultiplying an intermediate frequency band modulation signal from anintermediate frequency band modem by a local oscillation signal andtransmitting the signal; and a receiving unit for generating anintermediate frequency band demodulation signal downconverted bymultiplying a radio modulation signal by a local oscillation signal, anddemodulating the signal in the intermediate frequency band modem.
 6. Thefrequency hopping wireless communication system according to claim 5,further comprising one transmitting station for transmitting only thereference local oscillation signal.
 7. The frequency hopping wirelesscommunication system according to claim 5, wherein one of the pluralityof wireless communication terminals acts as a base station or a parentstation and transmits a local oscillation signal for use in the stationtogether with a radio modulation signal, and each child station which isone of the other wireless communication terminals receives a referencelocal oscillation signal transmitted by the base station or the parentstation.
 8. A frequency hopping wireless communication system forperforming communications in a frequency hopping system among aplurality of wireless communication terminals, characterized in that: inthe plurality of wireless communication terminals, a transmitting unitinputs to a mixer a modulation signal generated in an intermediatefrequency band and a frequency hopping signal obtained by a hoppingsynthesizer controlled by a hopping pattern generator, and obtains afrequency hopping radio signal; and amplifies an output signal of ahopping synthesizer used as a local oscillation signal in addition to afrequency hopping radio modulation signal of a single-side band wave ora both-side band wave by an amplifier without a band pass filter, andtransmits the signal through an antenna; and a receiving unit of thewireless communication terminal downconverts a received signal to afirst intermediate frequency band signal using a local oscillationsignal frequency hopping in a pattern obtained by adding a fixedfrequency offset to a frequency hopping pattern corresponding to adesired reception wave, and then, extracts two signal components, thatis, a local oscillation signal component and a modulation signalcomponent, by passing the downconverted signal through a band passfilter, and generates a product component of the two signal components,thereby regenerating a second intermediate frequency band modulationsignal.